JP2006-183864A published by the Japan Patent Office in 2006 discloses a steering damper interposed between handlebars and a vehicle body of a motorcycle to suppress unintended yaw or yaw oscillation of the front wheel while the motorcycle is running. This steering damper comprises a double-rod type damper cylinder and a damping force generating mechanism generating a damping force against the elongation/contraction of the damper cylinder, in a common housing.
The damper cylinder comprises a cylinder barrel and a piston enclosed in the cylinder barrel. Two piston rods are fixed to either end face of the piston and project outwardly in an axial direction from the cylinder barrel. A first oil chamber and a second oil chamber having an identical cross-sectional area are formed by the piston in the cylinder barrel.
The damping force generating mechanism comprises two valve bodies, i.e., a front valve body and a rear valve body, disposed coaxially in the housing. The two valve bodies are seated on two valve seats respectively. The rear valve body is biased by a solenoid actuator towards a closed position. The rear valve body is in contact with the front valve body so as to bias the front valve body towards a closed position.
Hydraulic pressure led from the first oil chamber in the damper cylinder is exerted on the front valve body towards an open position. Hydraulic pressure in the second oil chamber of the damper cylinder is led to a pressure chamber formed between the two valve bodies.
When the hydraulic pressure in the first oil chamber rises in accordance with displacement of the piston in a direction to compress the first oil chamber in the cylinder barrel, both the front valve body and the rear valve body retreat from the respective valve seats, and the working oil flows out from the first oil chamber, passes along an outer circumferential surface of the front valve body, and flows into the second oil chamber via the pressure chamber between the two valve bodies.
When, on the other hand, the hydraulic pressure in the second oil chamber rises in accordance with a displacement of the piston in a direction to compress the second oil chamber in the cylinder barrel, the pressure in the pressure chamber between the two valve bodies rises such that only the rear valve body retreats from the corresponding valve seat. As a result, the working oil flows out from the pressure chamber between the two valve bodies, passes along an outer circumferential surface of the rear valve body, and flows into a pressure chamber formed on the rear side of the rear valve body. This pressure chamber is connected to the first oil chamber via a check valve, and hence the working oil in this pressure chamber flows into the first oil chamber via the check valve.
The flow cross-sectional area of each of the two valve bodies when lifted varies according to the lift amount. By appropriately setting this relationship, the damping force generating mechanism can generate a preferable damping force in relation to the lift amount of the valve bodies.
The displacement of the piston in the cylinder barrel is damped by the damping force generated in this way.
This steering damper operates in a state where a cylinder barrel of the damper cylinder is engaged with one of a vehicle body and handlebars of a motorcycle while one of the piston rods is engaged with the other of the vehicle body and the handlebars of the motorcycle. The damping force generated according to the displacement of the piston in the cylinder barrel suppresses unintended yaw or yaw oscillation of the front wheel such that the riding comfort of the motorcycle is maintained.